We propose to characterize organ absorbed dose data for a large population of pediatric subjects who receive CT scans at our facility by matching real subjects with individuals in a large library of individuals of different age and body type developed from our existing realistic body models. We will manually segment images for 50 pediatric patients and calculate organs doses via Monte Carlo radiation transport calculations. Then we will develop a series of body models of children at various ages and of different Body Mass Index (BMI), to represent a range of normal variations in anatomy, using literature information and input from pediatric physicians. We will then modify our existing realistic phantoms of children of median size at the different standard ages (newborn, 1, 5, 10, and 15 year olds) to represent a number of body models that represent individuals of different size and stature and calculate organ doses for all of these models, using Monte Carlo transport methods. As new pediatric subjects are scanned, we will match each subject to the most similar NURBS model and report all organ doses and store this information for each subject. We will also match the 50 individual studies segmented with the most similar NURBS models and directly assess the difference between the organ doses from the direct calculations and those estimated from the nearest match individual, to understand the uncertainties in the day to day use of this approach. When completed and used regularly, this will allow characterization of organ and body radiation dose from a large population of pediatric subjects, for their own dose records, and for other uses, such as studies of medical subjects' population doses.